In a voltage driven (switching) element generally called a power device such as an IGBT or a power MOSFET failures can be caused by a short-circuit or so forth generated between a collector of the voltage driven element and an emitter thereof or, more specifically, a short-circuit generated in a load such as a motor connected between the collector and the emitter. Such a short-circuit causes an excessive current or an overcurrent to flow between terminals of the collector of the voltage driven element and the emitter thereof (or between a source of the voltage driven element and a drain thereof). This overcurrent can influence the life of the element. Accordingly, a protection circuit to protect the power device from such overcurrents is generally installed in a control circuit of such as a power inverter in which the load is driven using power devices.
Japanese Patent Application Publication (tokkai) No. 2002-353795 exemplifies a protection circuit of a voltage driven element in which a discharge from a gate electrode terminal of the voltage driven element is performed at a discharge current value proportional to a sensed current value proportional to conduction current flowing between the collector terminal of the voltage driven element and the emitter terminal. Thereby, the protection circuit prevents overcurrents due to a short-circuit failure or so forth generated in a collector circuit of the voltage driven element.